Fixed negativity in sqrt in costs.py by np.clip.

[OceanNuclear]

Description

Patches away the RuntimeWarning caused by sqrt(p_plant_electric_net_mw/1200), where p_plant_electric_net_mw may cross over to negative values briefly during the optimization process (but is expected to always converge on a positive value).

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made. (N/A)
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly. (N/A)
• I have added documentation for my change, if appropriate. (N/A)

[OceanNuclear]

Closes #4024

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.60%. Comparing base (ac78fdb) to head (4422c12).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4065   +/-   ##
=======================================
  Coverage   46.60%   46.60%           
=======================================
  Files         122      122           
  Lines       28711    28711           
=======================================
  Hits        13381    13381           
  Misses      15330    15330           

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[timothy-nunn]

@j-a-foster could you please provide a review here as you are Mr Cost Model. Does this change make sense and could it have any negative downstream impacts?